
 interface IList {
    void addFirst(int data);
    void addLast(int data);
    void addIndex(int index,int data);
    boolean contains(int key);
    void remove(int key);
    void removeAllKey(int key);
    int size();
    void clear();
    void display();
}

class MySingleList implements IList {
    @Override
    public boolean contains(int key) {
        ListNode cur = head;
        while(cur != null) {
            if(cur.val == key)
                return true;
            cur = cur.next;
        }
        return false;
    }
    @Override
    public int size() {
        ListNode cur = head;
        int sum = 0;
        while(cur != null) {
            sum++;
            cur = cur.next;
        }
        return sum;
    }
    @Override
    public void addFirst(int data) {

    }

    @Override
    public void addLast(int data) {

    }

    @Override
    public void addIndex(int index, int data) {

    }


    @Override
    public void remove(int key) {

    }

    @Override
    public void removeAllKey(int key) {

    }



    @Override
    public void clear() {

    }

    @Override
    public void display() {

    }

    static class ListNode {
        public int val;
        public ListNode next;

        public ListNode(int val) {
            this.val = val;
        }
    }

    //链表的属性  链表的头节点
    public ListNode head;//null

    public void createList() {
        ListNode node1 = new ListNode(12);
        ListNode node2 = new ListNode(23);
        ListNode node3 = new ListNode(34);
        ListNode node4 = new ListNode(45);

        node1.next = node2;
        node2.next = node3;
        node3.next = node4;
        this.head = node1;
    }

}
public class Main {
    public static void main(String[] args) {
        System.out.println("Hello world!");
    }
}